Due to widespread use of mobile terminals such as cellular phones and notebook personal computers, the role of the secondary batteries used for the power source thereof has increased importance. The secondary batteries are requested to have smaller size, lighter weight and higher capacity along with the stronger demand for larger-capacity, higher-speed communications and higher-speed transmission of color moving pictures.
For achieving the higher capacity of the secondary batteries, it is important to develop the electrodes, especially the anode active material thereof. Lithium-ion secondary batteries, wherein a metallic lithium foil is formed as an anode active material on a conductive substrate such as a copper foil by using a vacuum deposition process and a protective film is formed thereon, and higher-capacity secondary batteries having composite electrodes therein, wherein an active material having a larger theoretical capacity, such as silicon, is formed on a carbon-based film by using a vacuum deposition process, have been manufactured by trial, in order to achieve a higher energy density. For obtaining electrodes for such a higher-capacity secondary battery, it is tried to form an active material, which may provide a higher capacity, by using the vacuum deposition technology.
For manufacturing a large number of secondary battery electrodes by using the vacuum deposition technology, a continuous vacuum deposition technique is used wherein a conductive substrate (supporting member), such as a copper foil, is continuously supplied. In addition, for assuring the contact between the conductive substrate and a tab, the portion of the conductive substrate on which the tab is formed is preferably a non-evaporated portion, and thus the continuous patterning deposition technique is used.
There is a known technique wherein a stripe belt mask having therein openings arranged at a constant pitch along the longitudinal direction of the mask is carried while being in close contact with a metallic stripe belt, in order to continuously form a film pattern on the metallic stripe belt (Patent-Publications JP-A-1984-6372, 1984-84516, and 2000-183500). In this technique, the subject substance is formed on the metallic stripe belt through the openings of the mask, followed by winding up the metallic stripe belt and the mask separately.
In the technique described in JP-A-1984-6372, it is difficult to deposit the evaporated substance on the specified position of the metallic stripe belt because there is a large possibility that the mask and the metallic stripe belt have slack or bending due to the influences from the gravity and the tension by the sprocket. If a large tension by the sprocket is selected to avoid the influences, the openings of the mask will be possibly deformed or the metallic stripe belt will be possibly cut-off during the deposition process. In particular, in the step of deposition on the metallic stripe belt other than the feeding and winding steps thereof (refer to page 6 and FIG. 6 in the publication), the influences are more likely to occur because there is no mechanism (such as guide roller or can roll) for moderately pressing the metallic stripe belt and the mask.
In the technique described in JP-A-2000-183500, although the mask and the substrate are carried along the guide roll (evaporation roll) for effecting the pattern-deposition, the evaporated substance is deposited onto the mask during the iterated deposition process, whereby the deposited, evaporated substance may possibly be peeled off during the carriage to cause contamination or pollution. In addition, there are other problems that the mask is likely to be displaced or bent during the carriage, similarly to the technique described in JP-A-1984-6372.
Moreover, in the patterning by using those masks, there is another problem that a portion of the film is peeled off at the step of separation of the metallic stripe belt from the mask. In either of these cases, there is a need for providing the winding-up mechanism for the mask in the vacuum chamber, which causes the problems of a larger volume of the apparatus or a complicated structure of the apparatus. Further, since the evaporated substance is deposited on the mask in a mass production, as described before, the mask should be either replaced or cleaned for reuse, which causes a lower throughput of the process.
As described heretofore, there are large difficulties to manufacture the secondary battery electrodes in a mass production by using the conventional vacuum deposition apparatus and deposition process to continuously form patterns of the electrode active material for the secondary batteries on the conductive substrate such as copper foil.